IgA1 proteases are produced by members of the normal human oral flora. IgA is the principal carrier of antibody activity in secretions and has been shown to be involved in the protection of mucosal surfaces, including immunity to dental caries in model systems. The potential for interference with IgA-mediated mucosal immunity, with emphasis on anti-S. mutans antibodies, will be examined. The prevalence of IgA protease activity in plaque will be determined using a sensitive assay with IgA1 myeloma protein as a substrate. Since only the IgA1 subclass which constitutes approximately half of IgA in secretions is sensitive to these proteases, the distribution of antibody activity in parotid saliva against S. mutans antigens with respect to IgA subclass will be determined using an ELISA assay. Anti-S. mutans IgA has been shown to agglutinate S. mutans and inhibit glucosyltransferase activity. The consequences of IgA protease digestion on these activities will be investigated. Apparently intact Fab fragments of protease IgA have been shown to lose their ability to bind antigen. We intend to examine these fragments by N-terminal analysis for evidence of any additional cleavage that would result in this loss of activity.